Streams of exhaust or waste air and gas which occur in manufacturing plants contain in a number of cases hydrocarbons such as oils, petroleum fractions, benzines and solvents. Since the entrained hydrocarbons generally constitute a loss of operating material, the attempt has already been made at the point of formation to reduce or even to prevent the escape of these hydrocarbons. In most cases, however, the charging of the waste air with hydrocarbons cannot be reduced to values which are sufficiently low so as to comply to the amounts which are prescribed as highest permissible values in conformity with the protection of the environment or established law. Consequently, it is necessary for the discharged exhaust or waste air to be subjected to cleaning processes, which drastically reduce the concentration of the hydrocarbons which are contained in the said air and are to be classified as pollutants in the sense of the environment.
The pollutants can occur in exhaust air or gas flows in the form of gas or in the form of small drops. For separating out pollutants which are entrained in the liquid phase in the form of droplets, it is common to employ baffle separators, cyclones, demisters, electric separators or the like, which devices (depending on the design) may be capable of separating out droplets as small as 0.5 .mu.m.
However, it has proved to be difficult to separate out pollutants which are contained in the exhaust air in gaseous phase or even in the form of ultra-fine droplets. It is, of course, common to use activated carbon for separating out substances in the gaseous form. In connection with the large quantities of exhaust or waste air which occur, for example, during the running of a rolling mill and containing correspondingly large amounts of pollutants, filters which contain active carbon are extremely expensive. For example, it would be necessary for 50 liters of the pollutants per hour to be separated out, which pollutants (along with their additives) clog the carbon and make it unsuitable for use, so that a frequent change of filters becomes necessary and the removal of spent filter contant becomes a problem.
Some solid, liquid and gaseous pollutants can, of course, be removed from the waste air by means of conventional perforated plate scrubbers or washers operated with water, but the cleansing from the exhaust air of hydrocarbons such as oils, petroleum fractions, benzines and the like is impossible.
Thermal as well as catalytic post-combustion methods are also known in principle. Like the deposition of such gaseous pollutants in cooling traps, these cleaning processes cannot be used economically with exhaust or waste air which is formed in large quantities, since too large air quantities, heated to above the combustion/oxidation temperature of the pollutants, have to be cooled down to an optimal separation temperature or large quantities of catalysts (which have to be replaced relatively frequently) would have to be used.
The object of the present invention is to provide a process and apparatus by which large quantities of hydrocarbons along with the exhaust gas in which they are entrained are capable of being purified at an economically allowable expense.
With these and other objects in view, as will be apparent to those skilled in the art, the invention resides in the combination of parts set forth in the specification and covered by the claims appended hereto.